The cantilever type screen-printing machine is an important printing apparatus in the printing industry, and is particularly suitable for precision printing of circuit boards. The cantilever type screen-printing machine basically includes a base, a printing tabletop at a front portion of a top surface of the base, two cylindrical columns spaced at rear side of the base to serve as elevating rails, a transverse sliding assembly connected to and forward projected from the elevating rails to move up and down along the elevating rails, a printing head assembly connected to and forward projected from the transverse sliding assembly to move leftward and rightward along the transverse sliding assembly, and two cantilever arms separately connected to and forward projected from two ends of the transverse sliding assembly for supporting two screen plate holders thereon. With these components, it is possible to proceed printing on the printing tabletop through screen plates. Since the transverse sliding assembly, the printing head assembly, the cantilever arms, and the screen plate holders of the printing machine all are forward extended to locate in front of the elevating rails, and the elevating rails bear all loads of the components connected thereto, the printing machine is referred to as a cantilever type printing machine. Most of the currently available cantilever type screen-printing machines have similarly structured elevating rails and transverse sliding assembly that have become a standardized design of the screen-printing machines. However, following disadvantages are found in the above-described elevating rails and transverse sliding assembly for the currently available screen-printing machines:
1. The elevating rails includes two spaced cylindrical columns that tend to slightly bend forward due to insufficient rigidity when all the forward projected components connected to the front of the elevating rails are elevated along the elevating rails to a certain height from the printing tabletop. Actual measurement indicates that the magnitude of bending of the cylindrical columns under loads is in the range from 0.1 mm to 0.2 mm that is serious enough to adversely affect the high precision printing and prevent all the components forward projected from the elevating rails from smoothly moving up and down at high speed. PA0 2. Most of the transverse sliding assemblies for the conventional screen-printing machines are made of molded cast aluminum and have insufficient rigidity. In the case of providing a lengthened travel for the printing head, the conventional transverse sliding assemblies tend to deform and can not allow the printing head assembly to move along it at high speed. Moreover, the transverse sliding assembly formed from cast aluminum does not provide internal space for easy and good connection and/or mounting of other necessary components to the transverse sliding assembly. Components connected to outer surface of the transverse sliding assembly tend to be damaged during the printing operation. PA0 3. Being limited by formations of the elevating rails and the transverse sliding assemblies, the conventional screen-printing machine is pneumatically driven. The pneumatic driving mechanism provides insufficient brake force and speed that apparently fails to meet nowadays printing industry that asks for high speed, high productivity, and high efficiency. PA0 4. The conventional screen-printing machine usually has a pint thickness fine adjustment mechanism that includes a hand wheel mounted on a top of the elevating rails and a long screw rod connected at an upper end to the hand wheel and at a lower end to a cylinder seat. By turning the hand wheel, a cylinder on the cylinder seat and the transverse sliding assembly driven by the cylinder are finely adjusted in their vertical position. Since the hand wheel is located at a very high position on the top of the elevating rails, it can not be easily accessed and operated to accurately control the fine adjustment.